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ViragoTechForum.com XV750 Loss of power after 5500 revs ( SOLVED!!!!!)

#1: Great ! Loss of power after 5500 revs ( SOLVED!!!!!) Author: Kitt7 Post Posted: Mon May 24, 2010 9:04 am

Hi All, having slight problem with my New Old XV750, put new NGK iridium spark plugs in, starts easier and doesn't backfire, problem is when you give it full throttle after 5500 revs it seems to die off, still runs but loss of acceleration and top end???????

Last edited by Kitt7 on Mon May 31, 2010 11:39 am; edited 1 time in total

#2:   Author: grazingazer Post Posted: Mon May 24, 2010 9:44 am

could be fuel starvation due to partially clogged petcock filters or weakened petcock diaphragms...try running with the petcock in the prime position [switch it to on when you shut the engine down so you don't flood the crankcase with fuel] if it gives you more rpm range you need to clean the filters or rebuild/replace the petcock[s]...also make sure the fuel cap is venting properly

#3: Great ! Re: Loss of power after 5500 revs Author: Kitt7 Post Posted: Mon May 24, 2010 10:06 am

Thank You, i have ordered a petcock repair kit, had an idea it might be that, as there was fuel spurting out of seal, i fixed with instant gasket, well so i thought(duh). will try the prime position, great to hear from people with the knowledge. Thanks

#4:   Author: Kitt7 Post Posted: Mon May 24, 2010 1:28 pm

Quick update, tried the prime position still not go past 70mph, fine until 6000 revs. (maybe slightly better).
when i got her she ran fine then started to backfire on front cylinder, i adjusted the idle on front carb, 2.5 turns and put the new plugs in revs good until you drive ???????

#5:   Author: grazingazer Post Posted: Mon May 24, 2010 1:37 pm

if you're leaking fuel you're getting air in the fuel line...that pre-leans the mixture and reduces power...you might also have a vacuum leak causing further fuel dillution

#6:   Author: Kitt7 Post Posted: Mon May 24, 2010 1:45 pm

Thanks Again, will fit repair kit when it arrives, hopefuly tomorrow, then update,
i like her so much she will end up getting everything done, can't remember being so excited about something that's so economical to buy and for parts, think i'll be on this site for a while.

#7:   Author: Kitt7 Post Posted: Mon May 31, 2010 9:17 am

Fitted petcock repair kit, did both as they were inexpensive and for peace of mind, checked rubber vacum hoses, exhaust for leaks, all ok
Going better will sit at 70mph ok but open her up she does not really want to rev more than 6000rpm, revs ok when not moving.
One thing i noticed is when you touch one spark plug cap you get a shock but not the other, don't know if this has anything to do with it??????

#8:   Author: slowpoke Post Posted: Mon May 31, 2010 9:32 am

shouldn't get a shock. Buy a couple long right angle NGK plug caps (make sure they are for threaded posts or you will have to find your terminal caps for your plugs that you probably threw away), and about 3-4 feet of spark plug wire from your freindly neigborhood cycle parts shop (might as well get them there as they are inexpensive and if you ordered them in would cost more in shipping then the parts) and replace them. very easy to do.

#9:   Author: grazingazer Post Posted: Mon May 31, 2010 9:35 am

if the plug is fouling the spark will seek the path of least resistance in your case it may have been you...pull the plug on that cylinder and check it

#10:   Author: Kitt7 Post Posted: Mon May 31, 2010 9:35 am

No, i kept them, could this be the answer to my problems????

#11:   Author: slowpoke Post Posted: Mon May 31, 2010 9:38 am

Oh, and ya I concure with Graz. Sounds like fuel starvation, but could also be air starvation. May need to pull the petcocks out of the tank and clean the screens. Are there any in-line fuel filters? if so replace them. Also may want to check your air filter. make sure it is clean. If you don't know the history of the filter then replace it. Also sometimes I have heard of the air intake pipe getting sucked up to the bottom of the seat. Cut an inch or so off the end of that pipe and see how she runs.

#12:   Author: Kitt7 Post Posted: Mon May 31, 2010 10:02 am

No inline fuel filters and the screens/tank is very clean, the air filter is like new, will check air intake, Thanks, will update later.

#13:   Author: Kitt7 Post Posted: Mon May 31, 2010 11:38 am

SOLVED, YEEHA!!!!!!

It was air intake, after i got the bike i checked under the seat, as you do, when i pushed the seat in clip i knock a rubber knobbly bit (technical term) off the book holder, so the seat went to close to intake also my weight when sitting on her, THANKS FOR YOUR HELP, GREAT FORUM!!!!!!!!

#14:  Re: Loss of power after 5500 revs SOLVED!!!!! Author: grazingazer Post Posted: Mon May 31, 2010 11:48 am

Beers good call sp...prolly fouling the plug

#15:   Author: Matthew Post Posted: Mon May 31, 2010 12:09 pm

common problem for the 81-83 bikes, the rubber intake tube under the seat needs trimmed down or removed.

Still find mine kicking around the shop from time to time. I just give it the boot to another corner.

#16: Warning ! I DO NOT BELIVE! Author: BoPos Post Posted: Fri Jun 11, 2010 1:55 pm

Kitt7 wrote (View Post): SOLVED, YEEHA!!!!!!

It was air intake, after i got the bike i checked under the seat, as you do, when i pushed the seat in clip i knock a rubber knobbly bit (technical term) off the book holder, so the seat went to close to intake also my weight when sitting on her, THANKS FOR YOUR HELP, GREAT FORUM!!!!!!!!

I've looked for answer why my engine, couple days ago, doesn't turn over 5.000RPM. 3 times I've removed carburetors, checked everything, every diaphragm, jets, needles, intake boots and so on...
I even invent that this is ignition box problem... I saw that one guy re-solder this box due to ignition fault... Then I found this topic when I looked in our forum for 'cdi+repair'
doh
I've looked under my seat and, hmmmm..., this is very probable...
Tomorrow morning I will test how it run without rubber intake...
ViragoTechForum.com XV750 Loss of power after 5500 revs ( SOLVED!!!!!)


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